A known occupant protection system for a vehicle for protecting a vehicle occupant by, for example, causing an airbag to inflate immediately after a crash or a collision occurs, is suggested and practically in use. Pre-crash systems are also suggested and some of them are practically in use. In case the pre-crash system determines, before the crash, that the crash is unavoidable on the basis of a state of vehicle surroundings or vehicle behavior, the system causes a protection device to operate at an early timing. For example, a pre-crash system (an occupant protection system for a vehicle) disclosed in JP2007-500650A includes an adaptive seat that is controlled on the basis of a sensor signal. According to this pre-crash system, a recess is provided on a seat cushion, and a front portion of the seat is raised or a tensioning force of a seatbelt is increased by a belt tensioner at the time of a crash to prevent a submarine phenomenon, where the occupant slides forward so as to pass through a space between the waist seatbelt and the seat cushion at the time of the crash. In addition, a seat side support member is raised up at the time of the crash to prevent the occupant from being laterally slid. Further, a device including therein a cushion is deployed, in a manner of a collar, out of a headrest to prevent that the head of the occupant is moved by an impact of the crash.
A pre-crash system needs to detect any crash as early and accurately as possible so as to cause an actuator to actuate or move a seat, a seatbelt or the like. Therefore, for example, installing plural millimeter wave sensors is suggested to promptly determine a possibility of a frontal crash and a lateral crash. The system disclosed in JP2009-74803 includes one radar which detects an object in front of the own vehicle, and two radars which detect an object diagonally left and right forward of the own vehicle.
The actuator for moving or actuating the seat, the seatbelt or the like needs a period of time before it starts to actuate. The seat, the seatbelt or the like that are moved by the actuator also needs a period of time before it starts a mechanical operation. These periods of time are preferably as short as possible. One conceivable way to make the period shorter is to predict, instead of detect, the crash and to activate the pre-crash system. An occupant protection system disclosed in JP2007-314015 is able to modify a seated posture of the occupant depending on a type of crash upon detection of occurrence of the crash. For example, the vehicle is provided with plural cameras for a left lateral crash, a right lateral crash, and a rear-end crash. Image signals sent from the cameras are analyzed, and the occurrence of the crash is predicted on the basis of analysis results. Although a specific way of prediction is not described in the JP2007-314015, the occurrence of the crash is predicted by calculating a distance between the own vehicle and another vehicle, and the type of the crash. This calculation is performed on the basis of ever-changing information on position and speed of the another vehicle that is acquired from the another vehicle via a vehicle-to-vehicle communication.
When the crash is predicted and the pre-crash system is activated but no crash actually occurs, the seat, the seatbelt or the like is needlessly operated. If the seatbelt is repeatedly tightened and loosened, or the seat or the seatback is repositioned while driving, the occupant may perceive this as annoying. In a similar way, a warning may be perceived as annoying unless it is issued based on an accurate crash prediction and at an appropriate timing. For example, if the warning is issued too early, that is, if the warning is repeatedly issued even in case that the driver can reasonably avoid the crash by a normal driving maneuver, this may not only frustrate the driver but also decrease the driver's trust in the warning for a future occasion. Consequently, it is ideal that the crash is predicted with a high accuracy at an appropriate timing. It is also ideal that the pre-crash system is structured and controlled so as to provide a good response to the predicted crash. Improvement of accuracy of the crash prediction or response speed of the system, however, involves complexity in a mechanical structure of an actuator or a driven member, which may result in increase of costs.
A need thus exists for an occupant protection system for a vehicle, which is not susceptible to the drawback mentioned above.